Retina and superior colliculus from fetal rats will be transplanted to the tectal region of newborns. The patterns of afferent and efferent connections which they form with the host brain will be tested using a variety of anatomical techniques (autoradiography, degeneration methods for light and electron microscopy and horseradish peroxidase), as well as physiologically. By varying the age of the donor tissue and recipient animal, information should be provided on the role of timing in the development of specific neural connections. The interrelation of transplant and natural host afferents to the superior colliculus will be studied to investigate the role of competition in determination of the territories occupied by axon populations. The results of in vitro growth prior to transplantation will be studied as a preliminary to investigating the molecular basis of special affinities. These studies also test whether it may be feasible to use transplanted tissue as replacement for damaged regions.